(1) Field of the Invention
The present invention relates to a method for suppressing the growth of mycobacteria associated with hypersensitivity pneumonitis, in particular Mycobacterium immunogenum, in metalworking fluids. The method uses synergistic antimicrobial or biocidal compositions which include a metal complex comprising disodium monocopper (II) citrate and an isothiazolone mixture preferably comprising 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one. The present invention also relates to methods for detecting and identifying the mycobacteria.
(2) Description of Related Art
The prior art has described metal complexes of organic ligands as antimicrobial or biocidal compounds. These include U.S. Pat. No. 4,055,655 to Maurer et al., U.S. Pat. No. 4,129,589 to Shringarpurey et al., and U.S. Pat. No. 4,180,473 to Maurer et al. The process for their manufacture is described in U.S. Pat. No. 4,278,610 to Maurer et al. The problem is that these compounds are relatively poor antimicrobials and even large amounts provided protection for only a limited period of time.
The isothiazolones are described in U.S. Pat. No. 3,523,121 to Lewis et al.; U.S. Pat. No. 3,761,488 to Lewis et al.; U.S. Pat. No. 3,957,808 to Miller et al.; U.S. Pat. No. 4,105,431 to Lewis et al.; U.S. Pat. No. 4,243,403 to Lewis et al.; U.S. Pat. No. 4,252,694 to Lewis et al.; U.S. Pat. No. 4,265,899 to Lewis et al.; U.S. Pat. No. 4,279,762 to Lewis et al. These are very superior antimicrobial agents; however, relatively large amounts are required. Compatibility and stabilization of isothiazolones in metalworking fluids (MWF) has been described by Willingham and Derbyshire, J. Soc. Tribol. Lub. Eng. 47: 729–732 (1991).
Disodium monocopper (II) citrate (MCC) is particularly described as an antimicrobial compound by U.S. Pat. No. 4,055,655. Metalworking fluid (MWF) stabilizing activity is described in U.S. Pat. No. 4,129,509 (1978)). The former patent states that the compound is effective against microorganisms growing in alkaline environments (pH 8–12) due to the stability of the metal complex form only at high pH, with dissociation into toxic copper ions occurring upon encountering the lower pH (7.0) within microbial cells.
Studies on MCC have shown that it can temporarily inhibit the growth of Pseudomonas aeruginosa in laboratory media and transiently reduce the cell count in MWF contaminated with Pseudomonas spp. The use of MCC as a MWF additive is becoming more widespread and an improvement in its effectiveness was needed.
Although bacteria are highly important in the biodeterioration of MWF, fungi and yeast can play a major role as well, especially in the synthetic fluids (Bennett, Prog. Indust. Microbiol., 13: 121 (1974)), (Rossmoore and Holtzman, Dev. Indust. Microbiol., 15: 273–280 (1974)). Fusarium and Cephalosporium are prominent fungal contaminants, and among the yeasts, Candida and Trichosporon spp. are often isolated. Fungi and yeast are known to be sensitive to the toxic effects of Cu ion (Hugo and Russell, In: Principles and Practices of Disinfection, Preservation and Sterilization, Russell et al. (Eds.), Blackwell Scientific Publications, Boston, p. 69 (1982)) and consequently the effect of MCC at high pH on a representative yeast, Candida tropicalis, was studied.
As a result of the machining operation itself, MWF can become contaminated with selectively large concentrations of soluble iron. The high stability constant of ferric citrate can allow exchange reactions between the ferric and copper ions in binding to the citrate ligand (Ashcroft and Mortimer, Thermochemistry of Transition Metal Complexes, Academic Press, New York (1970)). Such reactions may destroy the antimicrobial activity of MCC in alkaline environments.
KATHON 886 is a commercial antimicrobial solution which is a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one (8.6% by wt.) and 2-methyl-4-isothiazolin-3-one (2.6% by wt.). The mixture is very effective against bacteria, fungi and algae. The required dosages are sometimes ineffective in achieving the best results due to interfering nucleophiles in the metalworking fluids. The molecular species considered as nucleophiles in these systems are amines and sulfides, the former contributed by many metalworking fluid formulae and the latter from microbial activity. Thus, efficacy is a function of the metalworking fluid composition as well as the level of microbial contamination, nucleophiles from both competing for the isothiazolones.
An important improvement in methods for suppressing growth of microorganisms in MWFs was introduced by U.S. Pat. No. 4,608,183 to Rossmoore. The patent discloses novel antimicrobial or biocidal mixtures comprising disodium monocopper citrate (MCC) and a mixture of isothiazolones. The components in the mixture were found to synergistically suppress growth of many species of bacteria and fungi in MWF over a long period of time. The synergism has been described in Rossmoore, Intl. Biodeter. 26: 225–235 (1990) and Sondossi et al., Intl. Biodeter. Biodegr. 32: 243–261 (1993). The compositions are particularly useful for metal cutting fluids wherein long duration antimicrobial activity is desired.
Over the past decade, it has been recognized that MWFs can be contaminated with mycobacteria as well as bacteria and fungi. It was further recognized that high levels of mycobacteria in MWFs appeared to coincide with outbreaks of hypersensitivity pneumonitis (HP) in industrial machinists (Kreiss and Cox-Ganser, Am. J. Ind. Med. 32: 423–432 (1997); Shelton et al., Emerg. Infect. Dis. 5: 270–273 (1999); Moore et al., AIHJ 62: 205–213 (2000)). Recently, a newly described species of mycobacteria, Mycobacobacterium immunogenum, was identified in MWFs associated with outbreaks of HP (Wilson et al., Int. J. Syst. Evol. Microbiol. 51: 1751–1764 (2001). More recently, a single genotype of Mycobacterium immunogenum was discovered to be present in MWFs associated with HP (Wallace et al., Appl. Environ. Microbiol. 68: 5580–5584 (2002)). A sample of the Mycobacterium immunogenum isolated from MWF was deposited at the American Type Culture Collection, 10801 University Boulevard, Manassas, Va. as ATCC 700506 and the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Germany as DSMZ 8223. Outbreaks of HP has continued even though MWFs are routinely treated with biocides. Therefore, there is a need for a method for treating MWFs which will suppress growth in MWFs the Mycobacterium immunogenum genotype responsible for the HP outbreaks. Preferably, the method would suppress growth of other bacteria and fungi as well.